1. Field of the Invention
This invention relates to oil filter means for an oil tank of hydraulic means, and more particularly means for removing the dusts, iron rust and water which remain on the bottom of the oil tank.
2. Description of the Prior Art
A hydraulic device which comprises an oil tank, a hydraulic pump and a hydraulic cylinder is used in various industrial fields. In an oil circulating passage of the oil pressure device foreign matters such as the dusts, iron rust, a water in the oil or the are deposited. More specifically, certain foreign matters are deposited in the hydraulic cylinder, and the iron rust, dusts and condensed water are deposited in the oil tank as well as in its piping.
If those foreign matters are not removed , the oil quality deteriorate and the hydraulic device may have operational troubles. Therefore, various oil filter devices are conventionally used to remove such foreign matters. However, when such an oil filter device is positioned in an oil return pipe between a hydraulic driving device and the oil tank, back pressure is increased, so that the hydraulic device cannot be operated smoothly. Thus, according to the conventional techniques, the foreign matters in the oil are removed by positioning such oil filter device in an oil supply pipe between the hydraulic pump on the oil tank and the hydraulic driving device such as the oil pressure cylinder or the like.
Although the foreign matters in the oil supply pipe can be removed, the foreign matters which are produced in the upstream side of the hydraulic driving device i.e. the oil return pipe as well as in the oil tank itself are deposited gradually on the bottom of the oil tank. Accordingly, unless the foreign matters on the bottom of the tank are removed, it is impossible to clean the oil completely and prevent it from being deteriorated.